Some embodiments relate to electromagnetic dosimetry, and more particularly, some embodiments relate to the measurement of electromagnetic dosimetric quantities in and on the surface of the human body.
The marketing of systems and devices emitting electromagnetic waves at varied emission powers requires obtaining a certain number of certifications of which some are aimed at ensuring the conformity of these devices with user exposure limits.
Various methods and techniques for evaluating the exposure of the human body to electromagnetic waves exist and vary in particular according to the frequency band used. When the frequency is high, the penetration depth of the waves in biological tissues (including in human tissues) decreases. It then becomes relevant to look more particularly at the level of exposure to a given electromagnetic radiation on the tissue surface and on the layers of the epidermis (and more broadly of the skin as a whole). Recent data transmission systems (including wireless) operate at high frequencies of up to several tens of gigahertz. These frequencies do not exist in nature, the effects thereof on human tissues remain relatively unknown or relatively uncharacterised to date.
The analyses already carried out by existing dosimetric methods, currently limited to frequencies of up to 6 GHz, conventionally use devices aiming to simulate the behaviour of the human body and particularly tissue absorption and reflection capabilities. These devices are commonly referred to as “phantoms”. Various categories of “phantoms” exist, such as, for example, “liquid phantoms”, “semi-solid phantoms” and “solid phantoms”. These laboratory devices make it possible to simulate various human tissue profiles having varied dielectric properties and are configured to enable testing in frequency ranges from 30 MHz to 6 GHz. “Liquid phantoms” can include or can consist of a casing (or shell) filled with a gel or a liquid having similar properties to those of the human body. They are generally used from 30 MHz to 6 GHz, but are only of little interest at frequencies greater than 6 GHz and in the millimetric wave range. Indeed, the penetration depth is merely approximately one half-millimetre at 60 GHz. Further “phantoms”, described as semi-solid, include water, and make it possible to simulate biological tissues such as muscles, the brain, the skin, for example, but suffer from a problem of longevity associated with a water evaporation phenomenon and the degradation of the resulting dielectric properties thereof.
Solid “phantoms” include ceramic, graphite or carbon elements, or synthetic rubbers and are essentially used for studies of the effects of radiation in and close to the surface of the human body. The main advantages thereof are the reliability thereof and the constancy of the dielectric properties thereof over time. Unfortunately, these solid “phantoms” have the disadvantage of being costly and requiring extreme conditions for the manufacture thereof, including particularly high temperatures and high pressures.
No solid “phantom” having electromagnetic properties equivalent to those of the human body (in terms of complex permittivity and conductivity) and operable above 6 GHz currently exists.
The document “Solid Phantom for Body-Centric Propagation Measurements at 60 GHz” (IEEE transactions on microwaves theory and techniques, VOL. 62, No. 6, June 2014) proposes a solid “phantom” based on a polydimethylsiloxane (PDMS) substrate including metallised carbon black powder on one of the sides thereof. This “phantom” is configured to simulate the behaviour of the human body on the surface, subjected to radiation in frequency ranges around 60 GHz. While the phantom described in this document offers good simulation capabilities of the reflection characteristics of human tissues on the surface, and particularly the skin, the measurements are made using sensors positioned at a certain distance from the “phantom”, due to the use of metallised shielding beneath the substrate. It is then easy to analyse the reflected wave (reflected signal) but it remains however impossible, using this “phantom”, to measure with precision the exposure levels such as the incident power density or the specific absorption rate.